Molding powder

ABSTRACT

A shaping material for a powder bed fusion method, including a powder of a fluororesin, wherein the fluororesin has a D50 of 30 μm or more and 200 μm or less, and the fluororesin has a D10 of 12 μm or more.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of International Application No.PCT/JP2019/017887 filed Apr. 26, 2019, claiming priority based onJapanese Patent Application No. 2018-087406 filed Apr. 27, 2018, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present disclosure relates to a three-dimensionally shaping powder,and particularly relates to a shaping powder which is used in a powderbed fusion method.

BACKGROUND ART

In recent years, an interest in a three-dimensionally shaping apparatus,a so-called 3D printer, has increased as a technique of shaping athree-dimensional structure. As a system regarding three-dimensionalshaping, for example, a vat photopolymerization method of performingshaping by irradiating a monomer of a photocurable resin in a vat withlight, a material extrusion method of performing shaping by extruding aflowable material from a nozzle to stack the flowable material, a binderinjection method of performing shaping by injecting a binder into apowder material to bind the powder material, an inkjet method ofperforming shaping by injecting a liquid resin and curing the injectedliquid resin, and a powder bed fusion method of performing shaping byirradiating a powder material with an energy ray to fuse and cure orsinter the powder material selectively, and the like are known. Amongothers, an interest in the powder bed fusion method has increased inrecent years.

Shaping by the above-described powder bed fusion method is generallyperformed in such a way that a powder material stored in a powdermaterial storage container is pushed and taken out with a recoater andis carried onto a shaping stand to form a thin layer of the powdermaterial, and this thin layer is irradiated with an energy ray toperform fusion. By repeating this operation, a three-dimensionalstructure is shaped. A production method and a production apparatususing such a powder bed fusion method are described in, for example,Patent Literatures 1 and 2.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Laid-Open No. 2017-007221-   Patent Literature 2: International Publication No. WO 2007/133912

SUMMARY OF INVENTION Technical Problem

A shaping material may be one of various materials, such asgeneral-purpose plastics and metals, in the powder bed fusion method,but shaping is difficult when a fluororesin is used as a shapingmaterial. In Patent Literature 2, the fluororesin is shaped by thepowder bed fusion method, but it is difficult to perform a good shapingsimply by shaping the fluororesin.

Therefore, the present disclosure aims to provide a novel shapingmaterial suitable for the powder bed fusion method.

Solution to Problem

The present inventors have found that controlling the volume accumulatedparticle diameter of the powder of the fluororesin improves the shapingby the powder bed fusion method.

The present disclosure includes the following embodiments.

-   [1] A shaping material for a powder bed fusion method, comprising a    powder of a fluororesin,

wherein the fluororesin has a D50 of 30 μm or more and 200 μm or less,and

the fluororesin has a D10 of 12 μm or more.

-   [2] The shaping material according to 1, wherein the fluororesin has    a D50 of 50 μm or more and 70 μm or less, and

the fluororesin has a D10 of 17 μm or more.

-   [3] The shaping material according to 1 or 2, wherein the    fluororesin has a D50 of 50 μm or more and 70 μm or less,

the fluororesin has a D10 of 17 μm or more, and

the fluororesin has a D90 of 130 μm or less.

-   [4] The shaping material according to any one of 1 to 3, wherein the    powder of the fluororesin has a static bulk density of 0.850 g/ml or    more and 1.500 g/ml or less.-   [5] The shaping material according to any one of 1 to 4, wherein the    powder of the fluororesin has a static bulk density of 0.950 g/ml or    more and 1.100 g/ml or less.-   [6] The shaping material according to any one of 1 to 5, wherein the    fluororesin is a tetrafluoroethylene-perfluoroalkoxyethylene    copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, or    an ethylene-tetrafluoroethylene copolymer.-   [7] The shaping material according to any one of 1 to 6, further    comprising a material other than a fluororesin.-   [8] The shaping material according to 7, wherein the other material    is a silica, a carbon fiber, graphite, a carbon nanotube, a carbon    nanohorn, fullerene, aluminum oxide, clay, montmorillonite, or talc.-   [9] The shaping material according to 7, wherein the other material    is a silica particle.-   [10] A powder of a fluororesin, having a D50 of 30 μm or more and    200 μm or less and a D10 of 12 μm or more.

Advantageous Effects of Invention

By using the shaping material of the present disclosure, athree-dimensional structure of a fluororesin may be suitably formed by apowder bed fusion method.

BRIEF DESCRIPTION OF DRAWINGS

The FIGURE is a perspective view of a molded body made in Examples.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a shaping material of the present disclosure will bedescribed.

A fluororesin contained in the shaping material of the presentdisclosure is not limited as long as it is a fluororesin that may beused in a powder bed fusion method, that is a fusible fluororesin. Thefluororesin may be preferably a thermoplastic fluororesin that isfusible with an energy ray including, for example, various types oflasers, such as, for example, CO₂ laser, fiber laser, and YAG laser, andis preferably CO₂ laser.

Examples of the fluororesin include, as a fluorine-containing olefinunit, one, or two or more of a tetrafluoroethylene (TFE) unit, achlorotrifluoroethylene (CTFE) unit, a vinyl fluoride (VF) unit, avinylidene fluoride (VDF) unit, a hexafluoropropylene (HFP) unit, atrifluoroethylene (TrFE) unit, a perfluoro(alkyl vinyl ether) (PAVE)unit, and fluorine-containing dioxoles. In one embodiment, examples ofthe PAVE unit include a perfluoromethyl vinyl ether unit, and aperfluoropropyl vinyl ether unit. In addition, examples of fluorine-freeolefin units include a hydrocarbon-based monomer having reactivity withthe above-described fluoroolefins. The hydrocarbon-based monomer ispreferably at least one fluorine-free olefin unit selected from thegroup consisting of, for example, alkenes, alkyl vinyl ethers, vinylesters, alkyl allyl ethers, and alkyl allyl esters.

In one embodiment, examples of the fluororesin include atetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), atetrafluoroethylene-hexafluoropropylene copolymer (FEP), anethylene-tetrafluoroethylene copolymer (ETFE), Neoflon EFEP (Trademark),a tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether)copolymer (PAVE), polychlorotrifluoroethylene (PCTFE), achlorotrifluoroethylene-tetrafluoroethylene copolymer, anethylene-chlorotrifluoroethylene copolymer, atetrafluoroethylene-vinylidene fluoride copolymer, a vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and avinylidene fluoride-hexafluoropropylene-copolymer. These fluororesinsmay be used alone or as a mixture of two or more thereof.

In a preferred embodiment, the fluororesin can be, for example, atetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), atetrafluoroethylene-hexafluoropropylene copolymer (FEP) or anethylene-tetrafluoroethylene copolymer (ETFE). These fluororesins may beused alone or as a mixture of two or more thereof. These fluororesinsare preferably used alone.

In one embodiment, the number average molecular weight of thefluororesin is not limited, and may be, for example, 100,000 or more and10,000,000 or less, preferably 500,000 or more and 5,000,000 or less. Ina preferred embodiment, the shaping material of the present disclosuremay be used in a powder bed fusion method, and therefore the fluororesinmay have a relatively low molecular weight of, for example, 3,000,000 orless, 2,000,000 or less, or 1,000,000 or less. By using alow-molecular-weight fluororesin, the mechanical strength of a shapedthree-dimensional structure is improved.

The melting point of the fluororesin is not limited, and may be, forexample, 100° C. or more and 350° C. or less, preferably 150° C. or moreand 330° C. or less. By setting the melting point of the fluororesin to100° C. or more, the heat resistance of a shaped three-dimensionalstructure is improved. In addition, the shaping temperature can belowered by setting the melting point of the fluororesin to 350° C. orless.

In the present disclosure, the above-described fluororesin is containedin the shaping material as a powder.

The present inventors have conducted studies on a shaping materialcontaining the above-described fluororesin and have noticed that toenhance shapability more, it is effective to make a thin layer which isformed with a recoater more uniform and to enhance the recoatability ofa powder of the fluororesin on a shaping stand. The recoatability of theshaping material can be changed by changing a property of the powder ofthe fluororesin, such as, for example, fluidity. For example, byenhancing the fluidity of the powder of the fluororesin, therecoatability of the shaping material can be enhanced.

In the shaping material of the present disclosure, the powder of thefluororesin has a D50 of 30 μm or more and 200 μm or less and a D10 of12 μm or more.

In one embodiment, the powder of the fluororesin may have a D50 of 30 μmor more and 200 μm or less, preferably 30 μm or more and 100 μm or less,more preferably 40 μm or more and 100 μm or less, still more preferably40 μm or more and 80 μm or less, and particularly preferably 50 μm ormore and 70 μm or less. By setting the D50 of the fluororesin to 30 μmor more, the fluidity of the shaping material is improved, and it makeseasy to form a uniform thin layer. By setting the D50 of the fluororesinto be larger, the fluidity of the shaping material can be enhanced more.In addition, by setting the D50 of the fluororesin to 200 μm or less, itmakes easy to obtain a smooth surface on a shaped three-dimensionalstructure. By setting the D50 of the fluororesin to be smaller, asmoother surface can be obtained on a three-dimensional structure.

In one embodiment, the powder of the fluororesin may have a D10 of 12 μmor more, preferably 13 μm or more, more preferably 15 μm or more, andstill more preferably 17 μm or more. By setting the D10 of the powder ofthe fluororesin to 12 μm or more, the fluidity of the shaping materialis improved, and it makes easy to form a uniform thin layer. By settingthe D10 of the powder of the fluororesin to be larger, the fluidity ofthe shaping material can be enhanced more. In addition, the upper limitof the D10 of the powder of the fluororesin is more preferable as it iscloser to D50 and is not limited. The closer D10 is to D50, the more thefluidity of the shaping material is improved, and it makes easy to forma uniform thin layer. For example, the D10 of the powder of thefluororesin may be 50 μm or less, 30 μm or less, or 20 μm or less.

In a preferred embodiment, the powder of the fluororesin has a D50 of 50μm or more and 70 μm or less and a D10 of 17 μm or more.

In one embodiment, the powder of the fluororesin may have a D90 ofpreferably 50 μm or more and 500 μm or less, more preferably 60 μm ormore and 200 μm or less, still more preferably 80 μm or more and 150 μmor less, and particularly preferably 90 μm or more and 130 μm or less.By setting the D90 of the powder of the fluororesin to 50 μm or more,the fluidity of the shaping material is improved, and it makes easy toform a uniform thin layer. By setting the D90 of the powder of thefluororesin to be larger, the fluidity of the shaping material can beenhanced more. In addition, setting the D90 of the powder of thefluororesin to 500 μm or less makes it easy to obtain a smooth surfaceon a shaped three-dimensional structure. By setting the D90 of thepowder of the fluororesin to be smaller, a smoother surface can beobtained on a three-dimensional structure.

In a preferred embodiment, the powder of the fluororesin has a D50 of 50μm or more and 70 μm or less, a D10 of 17 μm or more, and a D90 of 130μm or less.

The “D10”, “D50”, and “D90” herein refer to so-called volume accumulatedparticle diameters, and refer to particle diameters where cumulativevalues are 10%, 50%, and 90% respectively when they are arranged fromsmallest in a cumulative curve assuming the whole volume to be 100% in aparticle size distribution determined on a volume basis. In the presentdisclosure, the particle diameters are measured by a laser diffractionmethod.

In one embodiment, the static bulk density of the powder of thefluororesin may be preferably 0.850 g/ml or more and 1.500 g/ml or less,more preferably 0.900 g/ml or more and 1.300 g/ml or less, and stillmore preferably 0.950 g/ml or more and 1.100 g/ml or less. By settingthe static bulk density of the powder of the fluororesin to 0.850 g/mlor more, a volume change that occurs when the fluororesin is fused to beshaped can be made small. By setting the static bulk density of thefluororesin to be larger, the volume change at the time of shaping canbe made smaller. In addition, by setting the static bulk density of thepowder of the fluororesin to 1.500 g/ml or less, the fluidity of theshaping material is improved, and it makes easy to form a uniform thinlayer. By setting the static bulk density of the fluororesin to besmaller, the fluidity of the shaping material can be enhanced more. Itis to be noted that in the present disclosure, the static bulk densityis measured by the method described in JIS K6891.

In one embodiment, the Hausner ratio of the powder of the fluororesinmay be preferably 1.10 or more and 1.30 or less, more preferably 1.20 ormore and 1.25 or less. By setting the Hausner ratio of the powder of thefluororesin to be within the range, the fluidity of the shaping materialis improved, and it makes easy to form a uniform thin layer. The“Hausner ratio” herein refers to a ratio represented by tappeddensity/static bulk density. It is to be noted that the Hausner ratio inthe present disclosure is measured with a powder tester (manufactured byHOSOKAWA MICRON CORPORATION).

In one embodiment, the sphericity of the powder of the fluororesin maybe preferably 0.60 or more, more preferably 0.60 or more and 0.98 orless, still more preferably 0.70 or more and 0.95 or less, and furtherstill more preferably 0.80 or more and 0.95 or less. By setting thesphericity of the powder of the fluororesin to be within the range, thefluidity of the shaping material is improved, it makes easy to form auniform thin layer.

The “sphericity” herein refers to deviation of the powder from a sphere,and refers to an average value of a ratio of the maximum diameter ofeach particle to the short diameter that is orthogonal to the maximumdiameter (maximum diameter/shorter diameter) for arbitrary 50 particlesin a photographic projection obtained by taking a photograph with atransmission electron microscope. The powder gets closer to a sphere asthe sphericity gets closer to 1.

The powder of the fluororesin which is used in the present disclosure isnot limited, and may be produced by, for example, a method including thefollowings.

Polymerizing a fluorine-containing ethylenic monomer by suspensionpolymerization, thereby obtaining a powder of a fluorine-containingpolymer as polymerized,

optionally increasing the density of the powder as polymerized with aroll under a condition capable of obtaining a specific gravity of 90% ormore of true specific gravity, thereby obtaining a pulverized powder,

placing the powder as polymerized or the pulverized powder into afriction type mill,

processing the powder as polymerized or the pulverized powder into adesired shape, and

collecting a fluorine-containing polymer powder from the friction typemill.

The fluorine-containing polymer powder which is obtained by theabove-described production method has been processed into a desiredshape with a friction type mill and therefore has a spherical shape anda high static bulk density. The production method is more excellent inproductivity than a conventional method, and therefore a powder particlehaving a high static bulk density may be obtained in a highly efficientmanner.

Friction Type Mill

The friction type mill is an apparatus such that a plurality of vanes isarranged at an outer circumferential portion of a rotary shaft inside adrum, and a powder is fluidized in the drum by the rotating of thesevanes to cause centrifugal diffusion and vortex flow actions. The powderis received to mechanical stress by being pressed to an inner wall ofthe apparatus. A stirring member having a function of feeding andreturning the powder to and from a rotational shaft direction may beoperated. It is preferable to perform processing at a temperature of thefluorine-containing polymer powder in a range of 50 to 200° C.

Further, the friction type mill is preferably a friction type mill whosespecifications are such that: the mill includes a rotor provided with aplurality of blades at the outer circumference thereof, and a casingprovided with a cylindrical inner circumferential surface adjacent totip portions in the radial directions of the blades; the blades adjacentto each other along the shaft center direction of the rotor are eachextended toward a different direction from the shaft center; and atleast one pair of blades adjacent to each other along the shaft centerare each inclined in a reverse direction to the shaft center. Such anapparatus, for example, an apparatus described in Japanese PatentLaid-Open No. 2010-180099 can be used.

In an apparatus having such specifications, large compressive force andshear force are applied to the powder between the tip portions in theradial directions of a plurality of blades and the inner circumferentialsurface of the casing, so that a powder having a high static bulkdensity can effectively be produced.

Examples of such an apparatus include NOBILTA manufactured by HOSOKAWAMICRON CORPORATION.

The shaping material of the present disclosure may contain an additionalmaterial other than the powder of the fluororesin.

Examples of the additional material include shaping auxiliaries, suchas, for example, silica (SiO₂) (for example, a silica particle or asilica glass fiber), a carbon fiber, graphite, a carbon nanotube, acarbon nanohorn, fullerene, aluminum oxide, clay, montmorillonite, andtalc. By adding a shaping auxiliary, especially silica, to the shapingmaterial of the present disclosure, the fluidity and shapability of theshaping material are improved.

In a preferred embodiment, the shaping material of the presentdisclosure may be a mixture of a fluororesin material and silica.

The content of the silica may be preferably 0.1% by weight or more and1.0% by weight or less, more preferably 0.1% by weight or more and 0.5%by weight or less, and still more preferably 0.1% by weight or more and0.3% by weight or less based on the whole amount of the shapingmaterial. By setting the content of silica to 0.1% by weight or more,the fluidity and shapability of the shaping material are improved. Bysetting the content of silica to be larger, the fluidity and shapabilityof the shaping material, and the mechanical strength of thethree-dimensional structure are improved more. In addition, by settingthe content of silica to 1.0% by weight or less, the content of thefluororesin can sufficiently be secured, so that the characteristics ofthe fluororesin can sufficiently be exhibited in a three-dimensionalstructure.

The silica preferably has a particle diameter equivalent to the particlediameter of the fluororesin.

Examples of other additional materials include a laser-absorbingcolorant. The laser-absorbing colorant is not limited as long as it is amaterial that can absorb laser light having a wavelength of around 1 μm,and may be carbon, a metal, a pigment, a dye, and the like. Preferably,carbon is used as a main component. The laser-absorbing colorantpreferably has an average particle diameter of about 10 μm and has aparticle diameter range of 2 μm or more and 40 μm or less. The contentof the laser-absorbing colorant in the shaping material is preferably ina range of, for example, 0.05% by weight or more and 0.20% by weight orless.

In one embodiment, the silica particle may have a D50 of 30 μm or moreand 200 μm or less, preferably 30 μm or more and 100 μm or less, morepreferably 40 μm or more and 100 μm or less, still more preferably 40 μmor more and 80 μm or less, and particularly preferably 50 μm or more and70 μm or less.

In another preferred embodiment, the shaping material of the presentdisclosure consists of a powder of a fluororesin.

Next, a method of shaping the shaping material of the present invention,the method using a powder bed fusion method, will be described.

A shaping apparatus using a powder bed fusion method is generallyprovided with a powder storage container that stores a shaping materialon both sides of a shaping stand where shaping is performed. The shapingapparatus is further provided with: a recoater that supplies the shapingmaterial in the powder storage container to the shaping stand to form athin layer; and a laser unit by which the thin layer is irradiated withlaser.

Firstly, the shaping material in a necessary amount is stored in thepowder storage container. Subsequently, the shaping stand is lowered bythe height corresponding to the thickness of the thin layer. On theother hand, the bottom of the powder storage container is lifted to putan appropriate amount of the shaping material up above the powderstorage container. This shaping material is carried onto the shapingstand by the recoater, and the recoater is moved in such a way as toscrape on the surface, thereby forming a thin layer on the shapingstand. Subsequently, the powder is cured by scanning laser light basedon a slice data of a three-dimensional structure to be shaped and fusingthe thin layer. By repeating this operation, layers corresponding to theslice data are formed sequentially, and thus the three-dimensionalstructure is shaped.

Preferably, the temperature of the powder in the powder storagecontainer which is a supply area and the temperature of the powder onthe shaping stand which is a shaping area are controlled appropriatelyin shaping according to the shaping material to be used. By controllingsuch temperatures, a more uniform thin layer can be formed, andmoreover, performing more precise shaping is enabled.

EXAMPLES

As shown in Table 1 below, as fluororesins, the powders of PFA, FEP,ETFE, and EFEP were prepared. Each powder was made into samples (theminimum thickness of the walls was 0.8 mm), as shown in the Figure, eachbeing a hollow cube having a length of one side of 60 mm, the hollowcube including inside thereof a hollow cube having a length of one sideof 30 mm, using a powder bed fusion type 3D printer. Table 1 also showsthe temperatures of the supply area and the shaping area at the time ofshaping, and the evaluation results on the recoatability and theshapability.

The recoatability was evaluated as ◯ when the powder could be spreadover the surface without any aggregation of the powder or roughness onthe surface of the shaping area occurring at the time of recoating, Δwhen aggregation or surface roughness less likely occurred, and × whenaggregation or surface roughness occurred.

The shapability was evaluated as ◯ when a shaped product with a smallwarp and a good surface condition was obtained, Δ when a shaped productwith a small warp was obtained, but a slight roughness on the surfacewas observed, × when the warp was large and a good shaped product couldnot be obtained.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 1Example 2 Item Unit PFA PFA PFA PFA PFA Static bulk density g/ml 1.0420.957 0.988 0.843 0.8 Particle size D10 μm 19.10 17.53 18.11 15.62 12distribution D50 μm 68.69 53.18 55.69 29.02 22 D90 μm 139.7 96.30 100.3550.31 50 Melting point ° C. 300 300 257 300 300 Shaping Supply area ° C.260 260 200 260 230 temperature Shaping area ° C. 280 280 230 280 260Recoatability — ∘ ∘ ∘ x x Shapability — Δ ∘ ∘ x x ComparativeComparative Comparative Comparative Example 3 Example 4 Example 5Example 6 Item Unit FEP FEP ETFE EFEP Static bulk density g/ml 0.801 0.90.9 0.6 Particle size D10 μm 13.53 8 25 11 distribution D50 μm 29.45 15220 36 D90 μm 60.78 47 420 100 Melting point ° C. 257 257 220 164Shaping Supply area ° C. 200 200 180 120 temperature Shaping area ° C.230 200 200 140 Recoatability — x x Δ x Shapability — x x x x

As a result of the above tests, in Comparative Examples 1 to 4 and 6,the powder was aggregated at the time of recoating, and the shapedproduct was warped. In addition, in Comparative Example 5, aggregationhardly occurred at the time of recoating, but the shaped product waswarped, and roughness on the surface of the shaped product was observed.In Example 1, the recoatability was good and the warp of the shapedproduct was also small, but a slight roughness was observed on thesurface of the shaped product. In Examples 2 and 3, the recoatabilitywas good, the warp of the shaped product was small, and a shaped producthaving a good surface condition could be obtained.

INDUSTRIAL APPLICABILITY

The shaping material of the present disclosure can suitably be utilizedfor shaping various products, especially for shaping by a powder bedfusion method.

1. A shaping material for a powder bed fusion method, comprising apowder of a fluororesin, wherein the fluororesin has a D50 of 30 μm ormore and 200 μm or less, and the fluororesin has a D10 of 12 μm or more.2. The shaping material according to claim 1, wherein the fluororesinhas a D50 of 50 μm or more and 70 μm or less, and the fluororesin has aD10 of 17 μm or more.
 3. The shaping material according to claim 1,wherein the fluororesin has a D50 of 50 μm or more and 70 μm or less,the fluororesin has a D10 of 17 μm or more, and the fluororesin has aD90 of 130 μm or less.
 4. The shaping material according to claim 1,wherein the powder of the fluororesin has a static bulk density of 0.850g/ml or more and 1.500 g/ml or less.
 5. The shaping material accordingto claim 1, wherein the powder of the fluororesin has a static bulkdensity of 0.950 g/ml or more and 1.100 g/ml or less.
 6. The shapingmaterial according to claim 1, wherein the fluororesin is atetrafluoroethylene-perfluoroalkoxyethylene copolymer, atetrafluoroethylene-hexafluoropropylene copolymer, or anethylene-tetrafluoroethylene copolymer.
 7. The shaping materialaccording to claim 1, further comprising a material other than thefluororesin.
 8. The shaping material according to claim 7, wherein theother material is a silica, a carbon fiber, graphite, a carbon nanotube,a carbon nanohorn, fullerene, aluminum oxide, clay, montmorillonite, ortalc.
 9. The shaping material according to claim 7, wherein the othermaterial is a silica particle.